Zlatko Sitar

Kobe Steel Distinguished Professor

  • 919-515-8637
  • Research Building I 217

Prof. Sitar founded the WideBandgaps research laboratory that is focusing on bulk and thin film growth, characterization, and device development in wide bandgap semiconductors: GaN, AlN, and their alloys. He has pioneered the III-nitride MBE process through the design of a unique ECR plasma source, developed, patented, and commercialized a process for growth of AlN crystals, which is currently the only commercial high-quality AlN crystal growth process in the world (commercialized by HexaTech, Inc.), developed, patented, and commercialized epi-ready wafers and device layer growth processes on AlN wafers, which are the basis for high-efficiency deep-UV lasers and light emitting diodes, invented and patented a process for growth of III-nitride lateral polar structures via MOCVD and proposed and demonstrated novel devices based on this invention, which include lateral p-n diodes, low contact-resistance field effect transistors, quasi phase matched structures for optical frequency doubling, and superjunction-based devices.

Prof. Sitar directs the Materials Research Center at NCSU and holds joint appointments in Physics Department at NCSU and Electrical Engineering at University of Nagoya, Japan. His collaborative network spans all four inhabited continents. Based on his research, he founded HexaTech, Inc., an NCSU spin-out focusing on AlN crystal growth and wafer production and Adroit Materials, Inc., who is focusing on the development of UV light emitting devices on the AlN platform and vertical devices on native GaN substrates.

Education

Ph.D. 1990

Materials Science and Engineering

North Carolina State University

M.S. 1987

Physics

University of Ljubljana, Slovenia

B.S. 1982

Physics

University of Ljubljana, Slovenia

Research Description

Highlights of recent research accomplishments: •Developed a scalable process and equipment for growth of AlN single crystals and processes for fabrication of AlN substrates thereof. This is an extremely challenging process due to the high temperatures involved (2400°C) and materials compatibility issues. This leading work on III-nitride substrate technology is internationally recognized; many aspects of this work are patented and the technology is being commercialized. •Demonstrated the first true lasing in the UV spectral range, showing low threshold, high slope efficiency, polarization of light, narrow line, cavity modes, and far field pattern. Achieved record high IQE and low lasing threshold in AlGaN-based structures. •Following a more than 30-year-long debate in the open literature, and several years of our own research, we have finally solved the puzzle of UV absorption in AlN; this is a key finding that enables this technology to move forward. We have shown for the first time that by the manipulation of the Fermi level during the growth of wide bandgap semiconductors, we can control on what sites the point defects incorporate and what complexes form; this is an enabling technology that turns wide bandgap materials that are otherwise considered insulators into useful semiconductors. Developed a model explaining how the position of the Fermi level influences incorporation of compensating point defects. The model has been successfully used to reduce compensation by 2 orders of magnitude. •Developed an environmentally friendly, hydrogenless MOCVD process for growth of III-nitrides, which uses 100-times less ammonia and achieves films of very high quality. The process is being patented. •Developed MOCVD process for growth of GaN and AlN with controlled polarity (c+ or c-) on the same wafer; so far, others are able to grow only the c+ polar films. This process opens completely new opportunities for device design and exploitation of polarization effects in III-nitrides. Designed and demonstrated lateral polarity p-n junctions, light emitting diodes, field effect transistors, and demonstrated quasi-phase matched second harmonic generation. This work is patented. •Directly measured and explained ballistic transport in III-nitrides – developed experimental setup for precise measurement of electron energies; the first measurements of this kind in any semiconductor.

Honors and Awards

  • RJ Reynolds Award for Excellence in Research, Teaching and Extension, 2012
  • Kobe Steel Distinguished Chair, 2008
  • Entrepreneurship and Leadership Award, 2006
  • Alcoa Foundation Distinguished Engineering Award, 2004
  • Office of Naval Research MURI award, 2001

Publications

Ultrawide-bandgap semiconductors: Research opportunities and challenges
Tsao, J. Y., Chowdhury, S., Hollis, M. A., Jena, D., Johnson, N. M., Jones, K. A., Kaplar, R. J., Rajan, S., Van de Walle, C. G., Bellotti, E., Chua, C. L., Collazo, R., Coltrin, M. E., Cooper, J. A., Evans, K. R., Graham, S., & Grotjohn, T. A. (2018), Advanced Electronic Materials, 4(1).
Point defect reduction in MOCVD (Al)GaN by chemical potential control and a comprehensive model of C incorporation in GaN
Reddy, P., Washiyama, S., Kaess, F., Kirste, R., Mita, S., Collazo, R., & Sitar, Z. (2017), Journal of Applied Physics, 122(24).
Defect quasi Fermi level control-based C-N reduction in GaN: Evidence for the role of minority carriers
Reddy, P., Kaess, F., Tweedie, J., Kirste, R., Mita, S., Collazo, R., & Sitar, Z. (2017), Applied Physics Letters, 111(15).
Defect quasi Fermi level control-based C-N reduction in GaN: Evidence for the role of minority carriers
Reddy, P., Kaess, F., Tweedie, J., Kirste, R., Mita, S., Collazo, R., & Sitar, Z. (2017), Applied Physics Letters, 111(15).
Step-free GaN surfaces grown by confined-area metal-organic vapor phase epitaxy
Shelton, C. T., Bryan, I., Paisley, E. A., Sachet, E., Ihlefeld, J. F., Lavrik, N., Collazo, R., Sitar, Z., & Maria, J. P. (2017), APL Materials, 5(9).
Nonlinear analysis of vanadium- and titanium-based contacts to Al-rich n-AlGaN
Haidet, B. B., Sarkar, B., Reddy, P., Bryan, I., Bryan, Z., Kirste, R., Collazo, R., & Sitar, Z. (2017), Japanese Journal of Applied Physics, 56(10).
Optical signatures of silicon and oxygen related DX centers in AlN
Thonke, K., Lamprecht, M., Collazo, R., & Sitar, Z. (2017), Physica Status Solidi. A, Applications and Materials Science, 214(9).
Optical nonlinear and electro-optical coefficients in bulk aluminium nitride single crystals
Majkic, A., Franke, A., Kirste, R., Schlesser, R., Collazo, R., Sitar, Z., & Zgonik, M. (2017), Physica Status Solidi. B, Basic Solid State Physics, 254(9).
Model for the deep defect-related emission bands between 1.4 and 2.4 eV in AlN
Lamprecht, M., Jmerik, V. N., Collazo, R., Sitar, Z., Ivanov, S. V., & Thonke, K. (2017), Physica Status Solidi. B, Basic Solid State Physics, 254(8).
High free carrier concentration in p-GaN grown on AlN substrates
Sarkar, B., Mita, S., Reddy, P., Klump, A., Kaess, F., Tweedie, J., Bryan, I., Bryan, Z., Kirste, R., Kohn, E., Collazo, R., & Sitar, Z. (2017), Applied Physics Letters, 111(3).

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